ntp: security update, and use libcrypto

http://support.ntp.org/bin/view/Main/SecurityNotice#Recent_Vulnerabilities

The package would no longer build without libcrypto,
and it wouldn't find it without pkgconfig.
I checked that Debian and Arch do use openssl as a dependency,
so it's probably not so bad a thing to have.

CC maintainer @edolstra.

pkgs/tools/networking/ntp/default.nix

@@ -1,21 +1,19 @@
-{ stdenv, fetchurl, libcap }:
+{ stdenv, fetchurl, pkgconfig, libcap, openssl }:
 
 assert stdenv.isLinux -> libcap != null;
 
 stdenv.mkDerivation rec {
-  name = "ntp-4.2.6p5";
+  name = "ntp-4.2.8";
 
   src = fetchurl {
     url = "http://www.eecis.udel.edu/~ntp/ntp_spool/ntp4/ntp-4.2/${name}.tar.gz";
-    sha256 = "077r69a41hasl8zf5c44km7cqgfhrkaj6a4jnr75j7nkz5qq7ayn";
+    sha256 = "1vnqa1542d01xmlkw8f3rq57y360b2j7yxkkg9b11955nvw0v4if";
   };
 
-  configureFlags = ''
-    --without-crypto
-    ${if stdenv.isLinux then "--enable-linuxcaps" else ""}
-  '';
+  nativeBuildInputs = [ pkgconfig ];
 
-  buildInputs = stdenv.lib.optional stdenv.isLinux libcap;
+  buildInputs = [ openssl ]
+    ++ stdenv.lib.optional stdenv.isLinux libcap;
 
   meta = {
     homepage = http://www.ntp.org/;